In all the times I have replaced vellums on banjos, I have never experienced this happening.
This occurred twice on this. I tightened the skin not excessively because they normally dry tighter. The first time I left it in the proximity (not too close) of my wood burner (going. Its Spring but still cold here). To eliminate the crinkle I had to tighten it down so much that the tension band sat much lower than I would like. I removed the head, re-soaked and reinstalled. This time the position of the band would allow for more tightening without it going too low. After installing the head again I hung it up towards the ceiling on a hook to take advantage of the warm air pooling. This morning I found the same result. Any thoughts?
I would suspect it is slipping around the flesh hoop, though a possibility if your flesh hoop is narrow is there may be room for it to pull up inside the tension hoop.
Edited by - mbanza on 10/01/2022 15:10:01
-The Cartoon Dog-
Perhaps uneven heat causing uneven stretching.
Possibly uneven drying? If I understand correctly, hanging by a hook from the ceiling would mean the skin was vertical, rather than laying flat horizontally. If the taut side was closer to the ceiling, and the wrinkled side was lower, differential in warmth due to warmer air rising (as well as some downflow of moisture within the skin) may have caused uneven drying and the effect you see in the photo.
My suggestion would be to keep the rim/skin oriented horizontally. Keep it raised up on blocks so there is airflow on both sides. Periodically flip the rim over, say every hour or two. Airflow is enough, extra heat is unnecessary. Allow the time.
When I tuck a head, I really nurse it through the first 12 hours or so. In addition to the periodical flipping, I do keep the tension hooks finger tight, evenly all around, as the skin dries, checking them every hour or so.
There are different dynamics as the skin dries. Yes, the skin generally tightens. Yet also the thickness of the skin decreases as it dries out, such as under the tension hoop and around the flesh hoop. The effect of this drying is that the tension decreases. That's why it's not enough to just let it dry unattended. You will also need to check the hooks periodically as well.
I personally don't move past finger tight for at least two days. The skin should be completely dry before working it up to final tension. Even then, best to take time, not try to get there all in one go.
In the past, when I have an un-insulated gas hot water cylinder, I usually put the pot assy on top so the warmth could dry the vellum. Doing it this way I never had any issues whatsoever. In the morning everything was nice and dry and tight. I suspect though this issue might have something to do with the flesh hoop I was using. It is difficult to get brass bar here for making hoops.
This is the most difficult part of mounting a skin had--positioning the flesh hoop so that when tightened the tension ring sits in the right place. I have found that this involves some trial and error. I am not sure why it would be puckerd when dry. Any I have done tighten and become snugger when dry. I would never subject a wet skin head to any extra heat, but rather set it to dry in a location away from any direct heat.
If the vellum is not of uniform thickness it may be drying unevenly. When I install a skin head, I always leave the edges long enough to readjust the tension at various stages of drying . I use pliers to pull it tight when the tension hooks are snug, but not tight. Leave the tension hoop evenly adjusted all around, well above the vellum so as to allow even tension as it is tightened after drying so the tension hoop does not pull down too far. The last head I did was not bleached and it was obvious where the thick are were. Perhaps a pre-mounted skin head would be beneficial in this case?
I’ve never had this before. In my experience the head drys very tight and just the act of drying pulls any kind of wrinkles out.
I set the hoop about an 1/8” to 3/16” proud of the rim which is enough to take the stretch out over then next few months.
Perhaps you have a poorly prepared head? They should be quite hard and smooth just from drying.
My favorite heads are the white ones from an eBay dealer that are very inexpensive. And always calf.
A drawstring can help to avoid folds and maintain an even pull across the head (threaded through holes punched in the dry vellum at 2-2.5cm spacing). The drawstring can either be released once hooks are in place or I tend to leave until the excess vellum has started to stiffen while keeping a check on the head tension.
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